Stem cell factor promotes proliferation of human primitive megakaryocytic progenitors, but not megakaryocytic...

The effect of soluble c-kit ligand (stem cell factor, SCF) on human megakaryocytopoiesis of the cells from umbilical cord blood was evaluated in a methylcellulose culture containing human plasma. SCF alone did not stimulate megakaryocyte colony formation by non-phagocytic mononuclear cells (NPMNC), but did so in combination with interleukin (IL)-3, dose-dependently. This stimulatory effect was exhibited more strongly on large megakaryocyte colonies than on small ones. The effects of SCF + IL-3 on the number and size of megakaryocyte colonies exceeded those of IL-6 + IL-3 or of IL-11 + IL-3. The synergistic interaction of SCF with IL-3 was confirmed by using CD34-positive cells. In particular, addition of SCF to the culture with optimal and suboptimal concentrations of IL-3, significantly increased mixed megakaryocyte colony formation as compared with IL-3 alone. Although SCF in combination with IL-6 or IL-11 induced megakaryocyte colonies from NPMNC, these interactions disappeared entirely in the culture using CD34-positive cells. IL-6 or IL-11 significantly increased the size and DNA content of megakaryocytes in the presence of IL-3, while SCF did not affect, or rather decreased, the DNA content. These findings suggest that SCF promotes more strongly the proliferation of primitive rather than mature megakaryocytic progenitors, but does not affect megakaryocytic maturation.